Conventionally, as a type of optical transmission device, there is an optical reception apparatus that includes a distortion compensation apparatus configured to compensate, by using digital signal processing, for waveform distortion of a received light signal (for example, see Japanese Laid-open Patent Publication No. 2010-178222). In addition, there is a tunable dispersion compensator configured to make up for degradation of transmission quality caused by chromatic dispersion in the transmission path of a received light signal (for example, see Japanese Laid-open Patent Publication No. 2004-007150).
The delay amount when the waveform distortion of a received light signal is compensated for through digital signal processing is higher than the delay amount when the waveform distortion is optically compensated by using a tunable dispersion compensator or a polarization mode dispersion compensator. However, in recent years, for example, with finance-related traffic that is in high demand such as share price information, low latency (low delay) is desired. For the above-mentioned low-latency traffic, optical compensation may preferably be adopted instead of compensation based on digital signal processing.
Incidentally, when constructing and installing a optical transmission apparatus, an apparatus with a configuration that carries out compensation by using digital signal processing is installed in some cases, for example, because the apparatus is inexpensive, low latency is not desired, or the like. In this case, while the optical transmission apparatus is operating, when low latency is requested in a channel, compensation for the channel may be switched from compensation using digital signal processing to optical compensation.
However, when compensation using digital signal processing is switched to compensation based on a tunable dispersion compensator in an operating optical transmission apparatus, an initial value for compensation is decided by scanning a wide variable chromatic dispersion bandwidth, and the initial value is set in the tunable dispersion compensator. The same applies to when compensation using digital signal processing is switched to compensation by a polarization-mode dispersion compensator. An initial value is decided by scanning the polarization, and the initial value is set in the polarization-mode dispersion compensator. In either case, control for deciding the initial value is complicated, and it takes time to scan the variable chromatic dispersion bandwidth or the polarization. Therefore, there is a problem in that starting the signal flow after the switch takes time.